Targeting glucosylceramide synthase synergizes with C₆-ceramide nanoliposomes to induce apoptosis in natural killer cell leukemia

Abstract

Natural killer (NK) cell leukemia is characterized by clonal expansion of CD3 − NK cells and comprises both chronic and aggressive forms. Currently no effective treatment exists, thus providing a need for identification of novel therapeutics. Lipidomic studies revealed a dysregulated sphingolipid metabolism as evidenced by decreased levels of overall ceramide species and increased levels of cerebrosides in leukemic NK cells, concomitant with increased glucosylceramide synthase (GCS) expression. GCS, a key enzyme of this pathway, neutralizes pro-apoptotic ceramide by transfer of a uridine diphosphate (UDP)-glucose. Thus, we treated both rat and human leukemic NK cells in combination with: (1) exogenous C₆-ceramide nanoliposomes in order to target mitochondria and increase physiological pro-apoptotic levels of long chain ceramide, and (2) 1-phenyl-2-palmitoylamino-3-morpholino-1-propanol (PPMP), an inhibitor of GCS. Co-administration of C₆-ceramide nanoliposomes and PPMP elicited an increase in endogenous long-chain ceramide species, which led to cellular apoptosis in a synergistic manner via the mitochondrial intrinsic cell death pathway in leukemic NK cells.

Keywords::

• NK-LGL leukemia
• ceramide
• glucosylceramide
• PPMP

Acknowledgements

We thank Nate Sheaffer, David Stanford and Vanessa Andes of the Cell Science/Flow Cytometry Core Facility, Robert Brucklacher of the Functional Genomics Core Facility, the Biostatistics Core, and Wade Edris of the Microscopy & Histology Core Facility at Penn State Hershey Cancer Institute/Milton S. Hershey Medical Center for their technical assistance.

Potential conflict of interest: Disclosure forms provided by the authors are available with the full text of this article at www.informahealthcare.com/lal.

This study was supported by National Institutes of Health Grants CA098472 and CA133525 (to T.P.L), Penn State Hershey Cancer Institute Startup Fund (to X.L) and Tobacco Settlement funds (to M.K.).